This invention relates to fuel cells, particularly to fuel cell electrodes having good creep resistance during operation in fuel cell stacks. Electrode creep resulting in a decrease in stack height is of particular concern in high temperature fuel cell units employing molten carbonate electrolyte.
A basic fuel cell includes an anode for contact with the fuel gas and a cathode for contact and reaction with an oxidant gas. The electrodes are separated by an electrolyte such as a porous matrix containing molten carbonate salts. Each electrode typically includes a layer of catalyst material, for instance a porous plaque of sinter bonded or compacted metal or metal oxide particles. A perforated sheet separates the catalyst from the second section of the electrode which includes channels for directing reactant gas to the catalyst. The catalyst layers are porous to permit the reactant gas to diffuse into contact with the catalyst material. In the electrochemical reaction that occurs, ions travel from the cathode through the electrolyte into the anode where the fuel is oxidized. This ionic flow drives an electrical current in an eletrical circuit external to the fuel cell.
Cathode catalyst materials such as nickel oxide or zinc oxide have been suggested. Alternate materials such as the perovskites including various oxygenates of lanthanum, for instance LaMnO.sub.3, LaCoO.sub.3 and various other cathode catalyst materials listed in U.S. Pat. No. 4,206,270 are of potential value for use in molten carbonate fuel cells. Anode catalysts of nickel and various other materials such as Ni-Cr and Cu are suitable for catalyzing the reaction of hydrogen gas at the anode.
A typical electrode structure is illustrated in FIG. 1 of the drawing. The electrode 10 includes a porous layer of catalyst material 11 supported on a perforated sheet 13 next to a generally comb shaped member 15 that defines channels 17 for reactant gas flow into contact with the catalyst. Member 15 is an electrically conductive member and serves as a bipolar separator sheet between electrode 10 and an adjacent electrode of opposite polarity. Additional channels (not shown) are arranged perpendicular to channels 17 to provide a second reactant gas to the adjacent electrode of opposite polarity.
The catalytic layers in electrodes as described above have been found to suffer compressive creep of between 5 and 50% in thickness when exposed to pressures of 100 to 300 kPa, temperatures of 600.degree.-700.degree. C. for periods of 100 to 400 hours operation. Such conditions may occur in the operation of a molten carbonate fuel cell stack. Compressive creep of this magnitude presents major problems in reactant gas sealing and other structural arrangements in a fuel cell stack.
Therefore in view of the above, it is an object of the present invention to provide an electrode for a fuel cell with improved compressive creep resistance under operating conditions of a fuel cell stack.
It is a further object to provide an electrode structure for containing electrode catalyst material and for providing reactant gas access to the catalyst material.
It is a further object to provide a fuel cell electrode including a coherent layer of catalyst material with improved creep resistance.
It is also an object of the present invention to provide a fuel cell with improved compressive creep resistance.
It is also an object to provide a method of preparing an electrode component for a fuel cell wherein the electrode component exhibits improved compressive creep characteristics.
It is a further object to provide a method for preparing a fuel cell in which intercell separators are made composite with the electrode component.